You'll likely be asked to do something such as a small teaching task, prepare a lesson plan, debate some educational issue. What ever it is they are likely to tell you before hand. So I would say make sure you are prepared. Be yourself, that's who they really want to see, and on my interview the admissions tutor said "you have all done the hard thing, you've all impressed us with your UCAS applications, now relax". This helped us!